Conversion operations and in particular extrusion methods for plastics are for a long time state of the art and are e.g. described in the book: W. Michaeli, Einführung in die Kunststoffverarbeitung, 4. Edition 1999, Carl Hanser Verlag Munich, page 85 ff. In FIG. 6.1.1 on page 85 the conceptional diagram of a tube extrusion apparatus is described. With extrusion speed the speed of the caterpillar take-off and the speed of the prepared hollow section transported thereby is meant, respectively, thus the production speed of the extrusion apparatus.
During the production of multi-layer tubes or hoses having a polyamide outer layer by means of extrusion it was found that the mechanical characteristics, like elongation at break and cold impact strength, are worsening, if the extrusion equipment is operated with higher speed (starting from 20 m/min, increasing to e.g. 60 to 80 m/min or higher). In the present connection, the drawdown speed of the caterpillar take-off after the cooling line and the calibration (which may be accomplished e.g. by means of water cooling) is meant with the extrusion speed. In addition, it is to be noticed that when operating the apparatus at a higher extrusion speed also the material output of the extruder must be of course adjusted proportionally higher at the same time, because even on the higher speed level a certain article with the same cross section and the same wall thickness and to the same diameter respectively shall still result. Thus, during the evaluation of the mechanical characteristics in the present case extruded articles of the same geometry are respectively compared.
The above specified effect, that at higher extrusion speeds the mechanical characteristics of the manufactured articles are worsening, is already known to experts for a long time and represents a disadvantage, because the extrusion speed is limited thereby. The critical point of the multi-layer tube is namely the outer surface, i.e. the surface section of the tube, which cools down most quickly from the outer and which orients itself more distinctly at higher speed. Consequently, due to the higher tension in the outer surface and the smaller elasticity when mechanically loaded, respectively, it begins to break earlier. The effect mentioned above is described by e.g. A. Carin et al. in Intern. Polymer Processing XX (2005), pages 305-311. Here one finds on page 310 the well-known relation that the orientation of the outer surface increases with increasing drawdown speed, i.e. the elongation at break decreases vice versa.
According to EP 0 245 125 B1, it has been tried to get the orientation in the outer surface to disappear by a complicated and not completely harmless subsequent treatment method i.e. by means of flaming calibrated tubes with following renewed cooling.
EP 1 452 307 A1 describes multi-layer automotive tubes, which are resistant to peroxide containing gasoline and which also comply to the usual requirements regarding cold impact and which have a simple and economical structure. The multi-layer tube is formed with an inner layer based on a mixture of polyamide homopolymers, and it additionally has a compatibilizer. The characteristic feature of EP 1 452 307 A1 is the fact that the inner layer is not formed based on only one polyamide homopolymer or based on a mixture of polyamide 6 copolymers, but from a blend of different non-mixable polyamide homopolymers, using a compatibilizer. If this blend is also used for the outer layer of a multi-layer line, as provided in EP 1,452,307 A1, the above mentioned effect also arises, that with increasing extrusion speed the elongation at break of the multi-layer tube is reduced.
GB 2 390 658 B describes multi-layer polymer tube or hose lines with an ethylene/vinyl alcohol copolymer (abbreviated EVAL or, in the English-speaking world, also designated as EVOH) barrier layer as well as with an outer layer of polyamide 612 or polyamide 610 and an inner layer of polyamide 6, polyamide 612 or polyamide 610. These above mentioned materials have a very good dimensional stability under heat and good barrier characteristics against hydrocarbons and have additionally good adhesion between the layers, i.e. the multi-layer tube is resistant against delamination. But even with these multi-layer tubes the well-known effect arises that the elongation at break is reduced at increasing extrusion speed.
DE 698 31 239 T2 describes multilayered structures based on polyamides, in particular tubes with multilayered structure, wherein at least one inner layer and at least one outer layer are provided. The outer layer is formed from a mixture of at least one copolyamide of the type 6/6-36 and at least a second thermoplastic polymer, i.e. of the type polyamide 6. The second polymer does not contain plasticizers or elastomers.
EP-A-1 559 537 describes a multilayered plastic tube with barrier characteristics for automobiles. The plastic of the substrate may consist of a blend of polyamides. Further, a barrier layer made of EVOH is provided. The outer layer of the multilayered fuel tube can additionally have a jacket by an outer protective layer, which consists of a thermoplastic elastomer (TP) and a thermoplastic polyurethane (TPU), respectively. This additional protective layer can be coextruded with the other layers and thereby becomes a component of the composite composite.
US 2002/0012806 A1 describes thermoplastic multilayered structures, which include inner layers made from polyamides or polyamide mixtures. The polymer mixtures can contain usual polyamide types without plasticizers.
EP 0 710 537 A2 describes a multilayered line or conduit, wherein the inner layer consists of polyamides and which outer layer consists of polyamides having a layer of EVOH disposed between. The mixtures of the layer materials do not contain plasticizers and/or polyamide elastomers.
DE 35 10 395 A1 describes multi-layer fuel tubes or hose lines with an alcohol barrier layer based on polyvinyl alcohol. In the direction to the inner flow channel a polyamide protective layer made of polyamide 11 or 12 is provided.
U.S. Pat. No. 5,960,977 A1 describes polymer hoses or tubes with corrugated segments.
Use of elastomer modified polymers has further become known in other areas of the state of the art e.g. in medical technology or with fiber-optic cables. DE 3 724 997 C2 describes the use of polyamide/polyamide elastomer mixtures in the production of polymer protective layers of fiber-optic cables. The coating of fiber-optic cables with a layer of polyamide/polyamide elastomer mixtures is accomplished according to DE 3 724 997 C2 using the extrusion method.
EP 0 566 755 B 1 further describes polyether amide hoses for medical instruments, which are extruded from a mixture of two polymers, of which one polymer is a polyether amide and the other one is a polyether ester amide or a polyamide.
DE 2 716 004 C3 describes mixable polyether ester amides based on laurinlactam with polyamide 12 for the production of flexible, cool impact mono tubes.
In DE 3 724 997 C2 and DE 2 716 004 C3 as well as in EP 0 566 755 B1 polyether amides with laurinlactam are used as monomer for the polyamide block. Appropriate modified mixtures with polyamide 12 are also mentioned in the book: Polyamid-Kunststoffhandbuch, 3/4, 1998, Carl Hanser Verlag, page 872, paragraph 8.3.3. These blends are showing a partial compatibility, which is based on the cocrystallization of the polyamide 12 blocks with the homopolyamide. In the three corresponding patents neither multi-layer conduits nor the compatibilization are mentioned. However, such a mixture would not adhere on barrier materials, in particular not on EVOH. Polyamides which cause adhesion to EVOH, are described for example in the EP 1 162 061 B1.
DE 3 916 001 A1 describes a four-component mixture of amorphous copolyamides, block polyether polyamides, block polyether ester polyamides and modified copolyolefines. The disadvantage of such mixtures, which contain amorphous copolyamides, is the lower resistance to chemicals, especially to zinc chloride, which must be achieved for fuel lines.